Dicarbonyl compounds having the carbonyl groups on adjacent carbon atoms have become particularly valuable in recent years. The quantities of the compounds that are used have increased, and continuous processes have become increasingly important. Glyoxal, in particular, has become a chemical produced in large quantities and is used in the paper industry and the textile industry. In the latter, glyoxal is used in the manufacture of resins to impregnate cellulosic fibres for the manufacture of garments and other textile goods that have "permanent press" or "easy care" finishes. High purity products are particularly desirable for these uses.
Processes that have hitherto been used for the manufacture of such dicarbonyl compounds, particularly glyoxal, involve the air oxidation of the corresponding dihydroxy compound. The oxidation is catalytic, but it will be clear to those of ordinary skill that there are many products that can be obtained by the oxidation of such dihydroxy compounds. Products that are found in substantial quantity include the hydroxy-monocarbonyl compound, and various compounds formed by carbon-carbon bond cleavage between the hydroxy-substituted carbon atoms. If either or both of the carbonyl groups of the desired product are aldehydic, the aldehydic group or groups may be oxidised to give carboxylic acid groups; for example, the products may include the .alpha.-hydroxy acids, and the .alpha.-carbonyl acids.
It is therefore important for an economic process to use a selective catalyst that gives a good yield of the dicarbonyl compound and relatively small quantities of by-product. It is also important for economic operation to produce the dicarbonyl compound with as large a conversion of dihydroxy compound for each pass through the reactor containing the catalyst as possible.
It has been proposed to use catalysts consisting of copper or of silver, or of silver and silver oxide to give the desired selective reaction conditions. The use of suppressants for undesirable reactions has also been proposed. Using these catalyst, high conversions per pass, approaching 100% result in the yields of by-products being undesirably increased. Optimisation will in general require relatively low conversions, which require recycling of the dihydroxy compound, and substantial quantities of by-products, which require separation, and are, in general, of lower value than the dicarbonyl compound and may be valueless.
It is an object of our invention to provide a process for the production of dicarbonyl compounds that gives a high conversion per pass. It is a further object of our invention to provide a process for the production of dicarbonyl compounds with low yields of by-products. It is an object of our invention to provide a process for the production of dicarbonyl compounds and for the purification thereof that produces a product of high purity. Other and further objects of our invention will be obvious to those skilled in the art from the following detailed description of our invention.